For traditional radiotherapy equipment, e.g. head gamma knife, it is usually to control the rotation of a source body and corresponding collimator body therein, by a rotation controller couple thereto, to open and close the radioactive sources. Obviously, the accuracy of synchronous or asynchronous rotation of the source body and the collimator body affects the accuracy of the actual radiation dose emitted to the patient's lesion, further affects the uniformity control of a dose field.
An existing head gamma knife employs a semi-closed-loop feedback detection technology for controlling the synchronous or asynchronous rotation, and the rotation accuracy of the head gamma knife is monitored through encoders self-contained in a servo motor on the loop. However, this detection method cannot accurately reflect the real-time position of the head gamma knife when it rotates, because the motor and the load thereof are composed of a multi-stage transmission chain such as a speed reducer, a gear, etc., and each stage of the transmission mechanism will amplify the rotation error and will eventually reduce the rotation accuracy of the head gamma knife.